Dust adhesion prevention system for image scanning system

ABSTRACT

In an image scanning system, a deflector is contained in a casing having a cover glass which transmits a scanning light beam deflected by the deflector. An air flow is formed in front of the cover glass to prevent dust adhesion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a dust adhesion prevention system for an imagescanning system, and more particularly to a system for preventing dustfrom adhering to a cover glass of a casing in which a deflector fordeflecting a scanning light beam is contained.

2. Description of the Related Art

In an image scanning system using a raster scan of a laser beam, thedeflector for deflecting a scanning light beam is generally contained ina casing having a cover glass which transmits the scanning light beam inorder to prevent dust from the entering the optical system including thedeflector. This prevents dust or the like from adhering to thereflecting surface of the deflector such as a rotary polygonal mirror orreflecting surfaces in the optical system downstream of the deflector.When dust adheres to the reflecting surfaces in the optical systemdownstream of the deflector, streaks appear in a recorded imagedescribed later.

Further the cover glass serves to prevent the reflecting surfaces of thepolygonal mirror from staining and to prevent air turbulence caused bythe polygonal mirror rotating at high speed from affecting the overalloptical system. Stain on the reflecting surface of the polygonal mirrorlowers the reflectivity of the polygonal mirror and causes shading orthe like. In the case of a color printer, stain on the reflectingsurface of the polygonal mirror can cause nonuniformity in color.Accordingly it is preferable to provide such a scanning system with acover glass.

However when such a cover glass accumulates dust, the scanning lightbeam is affected by the dust and the scanning performance deteriorates.That is, when the scanning light beam deflected by the deflector forraster scan passes through the cover glass, the intensity of thescanning light beam is reduced at the portion of the cover glass withthe dust thereon and the density of the recorded image is reduced at thesame place on the main scanning line, which results in streakingextending in the sub-scanning direction. A similar phenomenon occurs inan image reading system, and this is fatal for an image scanning system.

Accordingly when such streaking appears in an image, the system must bestopped for cleaning of the cover glass. However there are objects whichcannot be scanned again, e.g., a stimulable phosphor sheet for use inradiography, and accordingly deterioration in performance of such animage scanning should be avoided to the utmost.

Especially in the case of a system where recording is effectedcontinuously at high speed, there is produced a great loss before theoperator recognizes the defect due to dust on the cover glass and stopsthe system.

SUMMARY OF THE INVENTION

In view of the foregoing observations and description, the primaryobject of the present invention is to provide a system for preventingdust from adhering to a cover glass of a casing of an image scanningsystem.

Another object of the present invention is to provide a system forremoving dust adhering to the cover glass as well as preventing dustfrom adhering to the cover glass.

The dust adhesion prevention system for an image scanning system inaccordance with the present invention includes a means for forming anair flow in front of the cover glass, thereby preventing dust fromadhering to the surface of the cover glass.

The air flow may be an air flow blown on the surface of the cover glassand/or an air curtain formed in front of the cover glass. Further theair flow may be a flow of air which is generated when an enclosed spaceis formed in the vicinity of the surface of the cover glass with an airoutlet provided in a position remote from the surface of the cover glassand the space is pressurized so that air is discharged through the airoutlet.

It is preferred that the air flow comprises air supplied from inside theimage scanning system.

In one embodiment of the present invention, the cover glass isconductive and grounded so that charged dust cannot adhere to the coverglass. Further the cover glass may be charged to have the same polarityas charged dust so that charged dust cannot adhere to the cover glass.

In the system of the present invention, the air flow formed in front ofthe cover glass prevents dust from adhering to the surface of the coverglass.

When the air is blown on the surface of the cover glass, the air flowremoves dust adhering to the surface of the cover glass as well asprevents dust from adhering to the surface. When an air curtain formedin front of the cover glass is used together with the air flow blown onthe surface of the cover glass, the effect is increased.

When the air flow includes air supplied from inside the image scanningsystem, the air flow does not produce a temperature difference betweenthe air flow and the inside of the image scanning system or the casing,and accordingly flicker cannot be produced in the optical system.

When the cover glass is conductive and grounded, charged dust cannotadhere to the cover glass, whereby dust adhesion prevention effect isfurther enhanced. When the cover glass is charged to have the samepolarity as the charged dust, the charged dust cannot adhere to thecover glass.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a part of an image scanning systemin which a dust adhesion prevention system of the present invention isemployed,

FIG. 2 is a cross-sectional view of a dust adhesion prevention system inaccordance with an embodiment of the present invention,

FIG. 3 is a cross-sectional view of a dust adhesion prevention system inaccordance with another embodiment of the present invention,

FIG. 4 is a cross-sectional view of a dust adhesion prevention system inaccordance with still another embodiment of the present invention,

FIG. 5 is a cross-sectional view of a dust adhesion prevention system inaccordance with still another embodiment of the present invention,

FIG. 6 is a cross-sectional view of a dust adhesion prevention system inaccordance with still another embodiment of the present invention, and

FIG. 7 is a schematic cross-sectional view of a digital photographprinting system which is an example of a system to which an imagescanning system with the dust adhesion prevention system of the presentinvention can be applied.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, an image scanning system includes a rotary polygonal mirror 4which deflects a laser beam 2a emitted from a laser 2. The polygonalmirror 4 is contained in a casing 8 in order to prevent entrance of dustinto the optical system of the light scanning system including thepolygonal mirror 4. The casing 8 is provided with a cover glass 6through which the laser beam 2a travels. The laser 2 may also becontained in the casing 8.

In a dust adhesion prevention system in accordance with an embodiment ofthe present invention shown FIG. 2, a wide nozzle 10 which blows airdownward is provided above in front of the cover glass 6. The nozzle 10produces a constant downward air flow 12 like an air curtain in front ofthe cover glass 6, whereby dust is prevented from adhering to thesurface of the cover glass 6.

A part or all of the air flow 12 may be blown on the surface of thecover glass 6 as an air shower.

In a dust adhesion prevention system in accordance with anotherembodiment of the present invention shown in FIG. 3, an air duct 18having bifurcated air outlet is employed. Air discharged through theoutlet adjacent to the cover glass 6 is blown on the surface of thecover glass 6 as an air shower 14 and air discharged through the airoutlet remote from the cover glass 6 forms an air curtain 16 in front ofthe air shower 14. In order to isolate these air flows from the otherspace, covers 20 and 22 are provided. A fan 23 for blowing air isdisposed in an upper portion of the air duct 18 and a filter 24 isprovided at the upper end of the air duct 18 in order to prevent dust orthe like from entering the air duct 18, whereby the air flows includeclean air.

In a dust adhesion prevention system in accordance with anotherembodiment of the present invention shown in FIG. 4, a cover 25 whichencloses a space 26 in front of the cover glass 6 and has an opening 30at the front end thereof is provided to surround the laser beam 2a andto permit the laser beam 2a to pass therethrough. An air duct 28 forintroducing pressurized air into the space 26 is connected to the cover25 at a portion near the cover glass 6. The pressurized air introducedinto the space 26 from the air duct 28 flows near the cover glass 6 andflows out through the opening 30, thereby preventing dust from adheringto the cover glass 6.

The opening 30 may be provided with a shutter 31 which closes theopening 30 as shown in FIG. 5 when introduction of the pressurized airinto the space 26 is interrupted. The shutter 31 prevents dust fromadhering to the cover glass 6 when the fan 23 is stopped.

In the above embodiments, it is preferred that the air flow includes airsupplied from inside the image scanning system. In this case, since thetemperature of the air flow is equal to that in the system, the opticalpath of the optical system can be free from flicker due to fluctuationin refractive index.

The still another embodiment shown in FIG. 6 is similar to that shown inFIG. 3 but differs from that in that the cover glass 6 is of aconductive material and is grounded through a ground lead 32 to preventthe cover glass 6 from being charged, thereby preventing charged dustfrom adhering to the cover glass 6.

The cover glass 6 may be charged to the same polarity as surroundingdust by use of, for instance, a corona discharger (not shown) so thatcharged dust becomes hard to adhere to the cover glass 6.

Grounding the cover glass 6 or charging the cover glass 6 to the samepolarity as surrounding dust may be combined with any one of thearrangements shown in FIGS. 2 to 5 and may be used alone if desired.

Though the dust adhesion prevention system of the present invention canbe applied to various image scanning systems for image recording such asa laser printer, it is especially suitable for image recording systemsfor a high quality image. As an example of such an image recordingsystem, a digital photograph printer system in which a color image isrecorded on a photographic paper on the basis of an image signal readfrom a color film will be described with reference to FIG. 7.

In FIG. 7, an image signal S read from a photographic film and processedas required is input into a printer 60 for reproducing a visible image.The printer 60 includes a printing section, a developing section and adrying section. The printing section includes a hole punch unit 63 whichpunches a reference hole for positioning photographic paper 100 in thephotographic paper 100 in a continuous length disposed in a photographicpaper roll magazine 62, a sub-scanning system 64 which conveys thephotographic paper 100 in the longitudinal direction thereof(sub-scanning direction) taking the reference hole as a reference, anexposure scanner 61 which causes a light beam modulated by a signalmodulated by a modulator driver to scan the photographic paper 100 in amain scanning direction and a back recording unit 65 which records onthe back side of the photographic paper 100 image retrieval informationinput through a printer control interface.

The drying section comprises a cutter 66 which cuts each print from thephotographic paper 100 in a continuous length which has been exposed anddried and a sorter 67 which arranges the prints.

The modulator driver (not shown) modulates the light beam emitted fromthe exposure scanner 61 according to image data input.

The printer 60 is controlled by a CPU by way of a printer controlinterface. The sub-scanning system 64 conveys in the sub-scanningdirection the photographic paper 100 in continuous length extendingalong a predetermined path from the magazine 62. The hole punch unit 63is disposed on the path of the photographic paper 100 and punches thereference holes, which is used as a reference for synchronization, onthe side edge portion of the photographic paper 100 at intervalscorresponding to, for instance, one print length. In the printer 60, thephotographic paper 100 is conveyed using the reference holes as areference of synchronization.

While conveyed in the sub-scanning direction in this manner, thephotographic paper 100 is scanned in the main scanning direction with amodulated light beam from the exposure scanner 61. Thus the photographicpaper 100 is two-dimensionally scanned with the modulated light beam andis exposed to light imagewise. The sub-scanning speed is controlled bythe CPU to a value suitable for reproduction of the image insynchronization with the main scanning speed.

The exposed photographic paper 100 is conveyed to the back recordingunit 65. The back recording unit 65 receives image retrieval informationunique to each piece of the image data from the CPU and records theimage retrieval information, e.g., film number and exposure number,corresponding to each frame on the back side of the frame. Thedifference in position of the exposure scanner 61 and the back recordingunit 65 is absorbed by a soft sequence (e.g., a sequence disclosed inJapanese Unexamined Patent Publication No. 5(1993)-193609) using thereference holes punched in the photographic paper 100. The imageretrieval information may be recorded on a part of the front side of thephotographic paper 100, i.e., the surface to be exposed to light. Inthis case, it is preferred that the information be recorded outside theexposed region, e.g., on the edge portion.

The exposed photographic paper 100 is conveyed from the printing sectionto the developing section, and then, after predetermined development andwashing in the developing section, is conveyed to the drying section. Inthe drying section, the photographic paper 100 is dried and cut intoprints by the cutter 66 on the basis of the reference holes. The printsfor one film roll are stacked by the sorter 67 and returned to thecustomer together with the film which has been cut into film strips,each for six exposures.

In such a color printer, not only the sharpness of the image but alsofinish of color is important, and accordingly adhesion of dust to thecover glass which can result in streaking and nonuniformity in colorshould be avoided to the utmost. Thus, use of the dust adhesionprevention system of the present invention together with the cover glassis especially desirable.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A dust adhesion prevention system for an imagescanning system having a deflector contained in a casing, comprising:acover glass transmitting a scanning light beam; and means for forming anair flow in front of the cover glass; wherein said means for forming anair flow in front of the cover glass includes a bifurcated air outletwhich forms an air curtain in front of the cover glass and an air flowblown on the surface of the cover glass.
 2. The dust adhesion preventionsystem of claim 1, wherein the air flow is an air flow blown on thesurface of the cover glass.
 3. The dust adhesion prevention system ofclaim 1, wherein the air flow is an air curtain formed in front of thecover glass.
 4. The dust adhesion prevention system of claim 1, whereinan enclosed space is formed in a vicinity of the surface of the coverglass with an air outlet provided in a position remote from the surfaceof the cover glass and said means for forming an air flow forms the airflow by pressurizing the space so that air is discharged through the airoutlet.
 5. The dust adhesion prevention system of claim 4, wherein theair outlet is provided with a shutter which closes the air outlet whenthe air flow is not formed.
 6. The dust adhesion prevention system ofclaim 4, wherein the cover glass is conductive and grounded.
 7. The dustadhesion prevention system of claim 1, further comprising means forcharging the cover glass with the same polarity as dust.
 8. A dustadhesion prevention system for an image scanning system having adeflector contained in a casing, comprising:a cover glass transmitting ascanning light beam; means for grounding the cover glass, the coverglass being conductive; and said means for forming an air flow in frontof the cover glass includes a bifurcated air outlet which forms an aircurtain in front of the cover glass and an air flow blown on the surfaceof the cover glass.